The present invention relates to a device and method for motion estimation and compensation in video encoding.
Motion estimation is the process of determining motion vectors that describe the transformation from one 2D image to another; usually from adjacent frames in a video sequence. Motion estimation is an ill-posed problem as the motion is often in three dimensions but the images are a projection of the 3D scene onto a 2D plane. The motion vectors may relate to the whole image (global motion estimation) or specific parts, such as rectangular blocks, arbitrary shaped patches or even per pixel. The motion vectors may be represented by a translational model or many other models that can approximate the motion of a real video camera, such as rotation and translation in all three dimensions and zoom.
Closely related to motion estimation is optical flow, where the vectors correspond to the perceived movement of pixels. In motion estimation an exact 1:1 correspondence of pixel positions is not a requirement.
Applying the motion vectors to an image to synthesize the transformation to the next image is called Motion compensation. The combination of motion estimation and motion compensation is a key part of video compression as used by MPEG 1, 2 and 4 as well as many other video codecs. The present application relates to combinations of motion estimation and motion compensation algorithms.
For any given codec a particular motion estimation algorithm is used. More advanced codecs are able to vary parameters of the motion estimation algorithm dynamically during processing, say to compensate for different circumstances appearing in the video.
International Patent Application WO 2009/066284A2 teaches a codec that switches dynamically between several motion estimation algorithms. However it always uses a standard motion compensation algorithm so that it can work with a standard decoder.